The present invention is directed to a surveying instrument with multiple beam paths, and in particular, to a surveying instrument with multiple beam paths capable of different functions or different magnification characteristics. The multiple beam paths may be used to produce, for instance, coarse-lock and fine-lock beam paths, and/or camera beam paths.
In surveying, tacheometers are known, an example of which is referred to as a total station and which represent a combination of a theodolite with vertical and horizontal angle measuring systems and a distance meter. This distance meter is usually integrated into the telescope of the theodolite. A video tacheometer is an instrument that, in addition to the functions of a tacheometer, also comprises at least a video camera.
From DE-GM 90 07 731, a measuring instrument is known for determining the position of optoelectronically representable spatial points, which includes a measuring head with a target acquisition device and a distance-measuring device. The sighting axes of the target acquisition and distance-measuring devices are accurately aligned with each other and run to the axis of motion of the measuring head at a predetermined angle. In concrete terms, this instrument is equipped with a wide-angle camera and a telecamera placed on the distance meter and uses them as a sighting aid for the distance meter. The sighting axes of these cameras and of the distance meter run parallel and at a certain distance to one another. In other words, there exists a parallax between the axes. The disadvantage here is that the eccentricity of the cameras in relation to the tilt axis (elevation axis) has a negative effect both on the sighting of the distance meter and the angle-measuring device. The parallax needs to be taken into consideration in either case.
From EP 0 281 518 B1, a telescope for a video theodolite is known, which avoids the disadvantage that the parallax presents for angular measurement. The camera is connected to the telescope through an additional optical system. However, in order to cover any additional instabilities caused by the extra optics, a reference mark must be arranged in the graticule plane of the telescope and imaged via the extra optics. The considerable expenditure on the optical components required and the small field of view resulting from a camera connected to the telescope thus constitute disadvantages.
The disadvantage of a small field of view has been eliminated in a telescope described in Allgemeine Vermessungsnachrichten, Issue 2, 1993, pages 63 to 65, in connection with FIG. 3 thereof. Briefly, a switching prism is used to optionally place a second optical system with a shorter focal length in front of a CCD camera, so as to obtain a larger field of view. The second optical system, however, also lies in an eccentric position in relation to the telescope optics. Another disadvantage of this arrangement is the considerable expenditure on the optical components required.
An article by Feist et al., entitled “Elta S10 und Elta S20 von Zeiss, System-tachymeter einer neuen Generation” published in Vermessungstechnische Rundschau (60), Issues 2 and 3, April 1998, shows in FIG. 5 thereof, a telescope where the beam paths for an optical telescope, for a distance meter and for fine lock are on the same optical axis, i.e., they are arranged coaxially to each other. Once again, the considerable expenditure on the optical components and assemblies required, as well as the fact that the existing CCD camera cannot be focused represent disadvantages which make any use of it as a video tacheometer impossible.
Accordingly, it is the primary object of the present invention to eliminate the disadvantages of the prior art and to create a surveying instrument with several switchable imaging, measuring and/or observation beam paths. Moreover, it is an object of the present invention to provide an instrument that is capable of providing several beam paths at minimal expenditure on optical components, and which allows the switching of beam paths to a position of normal use with high accuracy and in as little time as possible.